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Am Fam Physician. 2012;86(9):798-802

Original Article: Anaphylaxis: Recognition and Management

Issue Date: November 15, 2011

to the editor: I enjoyed and appreciated this article, but there was one question I had that was not addressed. Is there any evidence to suggest that an allergic reaction, such as isolated urticaria, can “get worse” and pose a risk of future anaphylaxis?

Scenarios that I often encounter in my practice involve patients who were seen in an emergency department or urgent care setting who were either stung by a bee and had a large local reaction (but no systemic symptoms to suggest anaphylaxis) or had urticaria after exposure to an unknown allergen that was presumed to be food (again without cardiovascular or gastrointestinal symptoms suggesting anaphylaxis). These patients are often sent home with an epinephrine autoinjector and told that a future reaction is typically more severe. However, I wonder if there is evidence to support this assertion, or if this is simply a perpetuated medical myth?

in reply: Knowing what to do for a patient with a previous significant allergic reaction to an insect or food that does not meet the criteria for anaphylaxis (i.e., involvement of at least two organ systems1) is a clinical challenge. Trials on how to approach these patients are lacking; therefore, guidance is based on retrospective data and consensus opinion from allergy and immunology experts.25 Unlike allergies to medication, allergies to food and insects are particularly problematic because avoidance is difficult.25

In the United States, patients with allergies to insect stings are predominantly allergic to the Hymenoptera species, which includes bees, wasps, yellow jackets, and hornets.13 Systemic allergic reaction to an insect sting is the best understood pathophysiologic model for anaphylaxis.2,3 It is also the most predictable with regard to what is expected in future reactions.2,3 Large, local insect sting reactions are defined as skin reactions (e.g., erythema, pain, swelling) greater than 10 cm contiguous to the bite site.2,3 Persons who have large local reactions may actually have a decreased likelihood of anaphylaxis with future stings of 5 to 10 percent, compared with 17 percent in persons with asymptomatic sensitization to venom.3 Skin and serum venom-specific immunoglobulin E (IgE) testing and venom immunotherapy are not recommended in patients with large local reactions.2,3 Prescribing an epinephrine autoinjector is also not recommended.2,3

For patients with mild, single organ systemic reactions (e.g., urticaria, flushing, angioedema) not contiguous with the bite site, recommendations vary based on age. In patients younger than 17 years, the exposure may be protective.2,3 Therefore, IgE testing, immunotherapy, and epinephrine autoinjector prescription are not required.2,3 In patients 17 years and older, risk of future anaphylaxis is thought to be increased.2,3 In addition to an epinephrine autoinjector prescription, referral to an allergist for IgE testing, guidance on avoiding the specific insect species, and immunotherapy, when indicated, are recommended.2,3

In contrast to allergies to insect stings, food allergies are highly unpredictable.1,4,5 Epinephrine autoinjectors are currently recommended for all patients with a history of any IgE-type reaction (e.g., urticaria, upper airway restriction, angioedema) to food, even if it is a single organ reaction and does not meet anaphylaxis criteria.4,5 These persons should also be referred to an allergist for testing.4,5 Avoidance cannot always be ensured because food labels may be misleading and because restaurants do not always advertise all the ingredients in the food served.4,5 Although a positive result on IgE food allergy testing is not predictive of severity of the reaction, it may assist with food avoidance.4,5

It is important to remember that the greatest contributor to preventing mortality from anaphylaxis is timely administration of intramuscular epinephrine.1 Although anaphylaxis-related death is rare—with 150 cases annually in the United States related to food and fewer than 50 cases annually related to insect stings—level of risk is impossible to determine based on current data.15 Physicians should “inform, not alarm”5 patients at risk, and educate them in anaphylaxis symptom recognition, proper use of the epinephrine autoinjector, and allergen avoidance.15

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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